Keep previously saved threads after the user switches labels and don't touch them

[jmanuel1]

Why?

Ways I can foresee implementing this:

• Save the label associated with the thread, and preserve to-do items with a thread label different from the current label
• Know which label is being removed when a label is removed from a thread and modify the to-do list only if that label is the one currently selected by the user
  • I think the possibility that a label is removed from a thread while Mailspring is not running is a non-issue since Mailspring will tell us when it starts again
  • Another non-issue is if that happens while Mailspring is running and the plugin is inactive, because I don't think Todoer should be expected to know about anything that happens while it's inactive (which is the case now)

[jmanuel1]

Here's something I haven't thought about: What if we switch labels, remove the first label from a thread, and then switch back?

[jmanuel1]

I think in that case the to-do item shouldn't be removed.